Question: You have found the following ages (in years) of 4 seals. Those seals were randomly selected from the 33 seals at your local zoo: $ 11,\enspace 8,\enspace 3,\enspace 6$ Based on your sample, what is the average age of the seals? What is the standard deviation? You may round your answers to the nearest tenth.
Answer: Because we only have data for a small sample of the 33 seals, we are only able to estimate the population mean and standard deviation by finding the sample mean $({\overline{x}})$ and sample standard deviation $({s})$ To find the sample mean , add up the values of all $4$ samples and divide by $4$ $ {\overline{x}} = \dfrac{\sum\limits_{i=1}^{{n}} x_i}{{n}} = \dfrac{\sum\limits_{i=1}^{{4}} x_i}{{4}} $ $ {\overline{x}} = \dfrac{11 + 8 + 3 + 6}{{4}} = {7\text{ years old}} $ Find the squared deviations from the mean for each sample. Since we don't know the population mean, estimate the mean by using the sample mean we just calculated {16} + {1} + {16} + {1}} {{4 - 1}} $ {s^2} = \dfrac{{34}}{{3}} = {11.33\text{ years}^2} $ As you might guess from the notation, the sample standard deviation $({s})$ is found by taking the square root of the sample variance $({s^2})$ ${s} = \sqrt{{s^2}}$ $ {s} = \sqrt{{11.33\text{ years}^2}} = {3.4\text{ years}} $ We can estimate that the average seal at the zoo is 7 years old. There is also a standard deviation of 3.4 years.